KR100810369B1 - Ofdm method and apparatus for data reception - Google Patents

Abstract

When interpolating the transmission line characteristics of symbols with no SPs arranged from the received SP signals distributed in the time direction, interpolation of the transmission line characteristics is performed by interpolating the received SPs before and after the symbols to be interpolated. The delay time of the number symbol of the time interpolation method is reduced. When interpolating the transmission path characteristics at the receiving SP, the plurality of receiving SPs received in the past are multiplied by different predetermined coefficients, and then complexly added to each result, and the first extrapolation or synthesis of the receiving SP vectors at a predetermined coefficient ratio, etc. By the time direction extrapolation process, interpolation path characteristics of symbols for which no pilot carrier is arranged are interpolated.

OFDM, reception method, receiver, transmission line characteristics, interpolation

Description

OFFDM reception method and apparatus therefor {OFDM METHOD AND APPARATUS FOR DATA RECEPTION}

1 is a block diagram showing a configuration according to a first embodiment according to the present invention;

2 is a block diagram showing the configuration of an MFN repeater;

3 is a schematic diagram showing an arrangement of SPs;

4 is a block diagram showing an interpolation scheme of transmission path characteristics;

5 is a block diagram showing the configuration of a repeater;

6 is a block diagram showing the configuration of a temporal extrapolation path characteristic interpolator of the present invention;

7 is a schematic diagram showing an operation explanatory diagram of the SP extraction unit of the present invention;

8 is a schematic diagram showing an interpolation scheme from one receiving SP of the present invention;

9 is a schematic diagram showing an interpolation method by primary extrapolation of the present invention;

10 is a schematic diagram showing an interpolation scheme from three received SPs of the present invention;

Fig. 11 is a block diagram showing the construction according to the second embodiment according to the present invention.

(Explanation of the sign)

11: extrapolation path characteristic interpolator 21: receiving antenna

22: A / D converter 23: FFT unit

24: delay correction 25: transmission characteristic interpolation unit

26: equalizer 27: remodulation

28: D / A converter 29: transmit antenna

51: adaptive filter unit 52: error calculation unit

53: IFFT section 54: filter coefficient changing section

61: memory 62: SP extracting section

63: extrapolation part 64: frequency interpolation part

The present invention relates to a relay apparatus for receiving terrestrial digital broadcasting modulated by an orthogonal frequency division multiplexing (hereinafter referred to as OFDM) scheme and performing broadcast wave relay.

In recent years, in the field of wireless devices, the OFDM method has been in the spotlight as a modulation method that is strong in multipath fading and mobile transmission, and many application studies have been conducted in countries including Europe and Japan.

In Japan, in December 2003, UHF terrestrial digital broadcasting using the OFDM method was started. This development trend and method are described in the 1998 Journal of the Korea Information and Media Society. 52, no. It is described in detail in 11 (refer nonpatent literature 1).

However, in order to broadcast this terrestrial digital broadcast all over Japan, it is a broadcast which receives the main broadcast of the UHF band from a new country, and transmits the terrestrial digital broadcast again at a different frequency or the same frequency from the reception channel. A wave repeater is used.

The repeater, which retransmits to another frequency of the former, is mainly used in an MFN (Multi Frequency Network) environment. Repeaters retransmitting at the same frequency of the latter are mainly used in a single frequency network (SFN) environment, thereby improving frequency utilization efficiency.

Below, the outline | summary of an MFN repeater and SFN repeater is demonstrated.

First, the structure of the conventional MFN repeater is shown in FIG. 2, and the characteristic of an MFN repeater is demonstrated using FIG.

The signal received by the reception antenna 21 is sampled by the A / D 22, and then converted by the FFT unit 23 into a frequency axis signal, and the frequency axis signal r (t, k) (where , t: symbol number, k: carrier number). The transmission path characteristic interpolation unit 25 interpolates the transmission path characteristics from the new station to the reception antenna based on the pilot signal included in the received signal.

An interpolation algorithm of the transmission path characteristics will be described with reference to FIGS. 3 and 4. 3 is an explanatory diagram of a pilot signal employed in the terrestrial digital broadcasting system. The carriers indicated by the black circles in the figure are pilot carriers of known amplitude and phase, and are arranged in a distributed manner in the frequency (carrier) direction and the time (symbol) direction. Hereinafter, this pilot carrier is called SP (Scattered Pilot). When interpolating the transmission path characteristics of the symbol indicated by the arrow, it is possible to interpolate the received SP directly as the transmission path characteristics for the carrier into which the SP indicated by the black circle is inserted. It is necessary to interpolate to the carrier (data carrier) shown by the SP received back and forth in time.

The present invention relates to this interpolation algorithm, and will now be described in detail with respect to interpolation methods that are currently used.

Since the SPs are distributed, it is necessary to interpolate to the front and rear SPs for carriers without SPs, but as the interpolation method in this time direction, the first interpolation and the 0th hold are shown. The method is generally used.

The first interpolation is a method of interpolating interpolation of the SPs before and after the symbol to be interpolated in a straight line, and the 0th order is a method of replacing the SP to be interpolated with the SP of the symbol closest in time to the symbol to be interpolated.

By the interpolation method described above, the transmission path characteristics are interpolated using the SP, and the transmission path characteristics interpolation section 25 outputs the interpolation transmission path characteristics h (t, k).

The equalizer 26 complex-divides the output signal of the delay correction unit 24 provided to correct the delay with the transmission characteristic interpolation section 25 by the interpolation transmission characteristic h (t, k). Equalization of amplitude and phase (i.e., waveform equalization) is executed (or diversity synthesis based on interpolation transmission path characteristics instead of waveform equalization by the equalizing unit).

The equalized signal is subjected to IFFT processing by the re-modulator 27, and is again converted to a time-base signal, and generates an OFDM transmission signal by adding a guard interval. The OFDM transmission signal is analog-converted by the D / A 28 and transmitted from the transmission antenna 28 in a channel different from the reception channel.

Next, the structure of an SFN repeater is shown in FIG. 5, and the characteristic of an SFN repeater is demonstrated using this.

The signal received by the reception antenna 21 is transmitted from the transmission antenna 29 via the A / D 22, the adaptive filter 51, and the D / A 28. Here, since the transmission frequency and the reception frequency are the same, a part of the signal output from the transmission antenna 29 reaches the reception antenna 21 as a return wave. The adaptive filter 51 cancels this returning wave by adaptively controlling the filter coefficients. A large reason for performing waveform equalization by applying the adaptive filter to the time axis region is to shorten the propagation delay time from the reception antenna to the transmission antenna. This is because when the delay time between the received signal and the transmitted signal becomes longer, the transfer function of the entire repeater becomes unstable and the probability of waveform distortion or oscillation, etc. increases, so that from the reception antenna to the transmission antenna in order to solve this problem. This is because the delay time needs to be as short as possible.

In the filter coefficient update system, the output signal of the adaptive filter 51 is converted into a signal on the frequency axis by the FFT unit 23, and the channel interpolation unit 25 performs interpolation of the channel characteristics as described above. The error calculating unit 52 calculates a residual error between the interpolated SP signal and the known SP signal, and the IFFT unit 53 converts the frequency axis signal into a time axis signal again.

The filter coefficient updating unit 54 sequentially updates the coefficients so that the residual error is minimized. In this way, the inverse function of the transmission path function from the transmission antenna to the reception antenna is formed by the adaptive filter, and the return signal by the return wave can be canceled.

Also, in the OFDM receiver, interpolation is first performed in the frequency direction, and then first extrapolated in the time direction to interpolate the transmission line characteristics.

(Non-Patent Document 1) Journal of the Korean Society for Image and Information Media 1998 Vol. 52, no. 11

(Patent Document 1) Japanese Unexamined Patent Publication No. 2002-300094

The repeater described above is used as a fixed line, but fluctuations in the received signal occur due to reflection of the antenna and shaking of the antenna during a storm. The fluctuation in the received signal is a fluctuation in the transmission line characteristics. Further, in the MFN repeater and the SFN repeater, compensation is performed by interpolating the transmission path transfer function from the receiving SP and multiplying by the opposite characteristic of the interpolated characteristic. However, in an environment with such a large variation, when the SP interpolation in the time direction of the SP by the zero-order hold method as described above is performed, the error of the interpolated transmission path characteristics becomes large, resulting in deterioration of the equalization characteristics. In the interpolation method using the primary interpolation method, since the interpolation is performed at the front and rear SPs, at least three symbol delays occur at the SP intervals of the four symbols used in the terrestrial digital broadcasting method. In the terrestrial digital broadcasting parameter, a delay of about 3 ms occurs because one symbol is about 1 ms.

In an MFN repeater, this delay time is added to the main route of the repeater and cannot be ignored in a system with high demand for low delay. In the SFN repeater, since interpolation path characteristics are used to update the coefficients of the adaptive filter, when a high-speed fluctuation of the channel characteristics occurs, this delay time is a factor that lowers the stability of the system. . In other words, if the delay loop is included in the feedback loop formed for the coefficient update, the system loses stability and, in the worst case, oscillates.

In addition, since it is necessary to store data of several symbols before and after, there is a drawback that the required memory capacity is increased and the hardware scale is increased.

In addition, when interpolating the transmission path characteristics of a symbol in which no SP is arranged from the received SP signals distributed in the time direction, interpolation is performed from the front and rear receiving SPs before and after in the time direction of the symbol to be interpolated. Interpolation of transmission line characteristics was performed by first extrapolating in the time direction. However, in the method prior to this time interpolation, there has been a problem that a delay time of several symbols occurs.

In the present invention, in an OFDM receiver for receiving an OFDM modulated signal in which pilot carriers having known amplitude and phase are distributed in the time direction as a first method for solving the above problems, in the past p (p is an integer) within a symbol period. Q (q is an integer) received pilot carriers multiplied by independent predetermined coefficients, and then synthesized the respective results to extrapolate the transmission path characteristics of symbols without pilot carriers interpolated in the time direction. do.

As a second method, the above time extrapolation method performs first-order extrapolation on two pilot carriers received at a past time point closest to the symbol to be interpolated, thereby transmitting a symbol on which no pilot carrier is arranged. Interpolate the properties with.

As a third method, the above time extrapolation method multiplies a predetermined coefficient with respect to three pilot carriers received at a past time point closest in time to the symbol to be interpolated, respectively, by a predetermined coefficient, and then each result. Are synthesized and interpolated by extrapolating the transmission path characteristics of symbols having no pilot carriers in the time direction.

In addition, an OFDM receiver and an OFDM repeater having a channel interpolation scheme using the first to third extrapolation schemes described above are used.

A first embodiment according to the present invention will be described in detail with reference to FIG. In addition, the structure shown in FIG. 1 is a structure which replaced the transmission line characteristic interpolation part 25 with the time extrapolation transmission line characteristic interpolation part 11 in the MFN repeater by the prior art shown in FIG. It has a function.

First, the signal received from the reception antenna 21 is sampled by the A / D 22 to obtain a time base received sample value sequence. A time window is provided in which no symbol interference occurs on the time axis signal, and the signal in the time window is subjected to the frequency axis signal r (t, k) by the FFT unit 23 (where t: symbol number, k: Carrier number). The frequency axis signal r (t, k) is input to the time extrapolation transmission line characteristic interpolator 11 to calculate the interpolation transmission line characteristic h (t, k).

The present invention relates to the time extrapolation transmission line characteristic interpolation section 11, and the function of the time extrapolation transmission line characteristic interpolation section 11 will be described in detail below.

6 shows a configuration of the time extrapolation transmission path characteristic interpolation unit 11. The frequency axis signals r (t, k) from the FFT unit 23 are input to the delay unit 61 and the SP extracting unit 65. The delay unit 61 outputs a signal r (t-1, k) obtained by delaying the frequency axis signal r (t, k) by one symbol. The output signal r (t-1, k) of the delay unit 61 is input to the delay unit 62 and to the SP extracting unit 65 at the same time. The operation of the delay unit 62 is the same operation as the delay unit 61, and outputs a signal r (t-2, k) delayed by two symbols. Similarly, the delay unit 63 and the delay unit 64 output the three symbol delay signals r (t-3, k) and the N symbol delay signals r (t-N, k).

In order to interpolate the transmission path characteristics from the SP carrier received at the time extrapolation section 66 at the later stage, the SP extracting section 65 is received at the present time or the past time, which is an output signal of the delay units 61 to 64. The SP carrier is extracted from the frequency axis signal and output. Specifically, when the interval between the SP carriers in the time direction is four symbols, for example, the signals r (t, k), r (t-1, k), r (t-) from the delay parts 61 to 64; SP signals extracted from 2, k), r (t-3, k), ..., r (tN, k),

r (t ', k), r (t'-4, k), r (t'-8, k), r (t'-12, k), ..., r (t'-4 × i , k)

Becomes Here, when the interpolation target is the k-th carrier from the t symbol time point, t 'represents the symbol time point closest to t in which the SP exists among the past N symbols. In addition, since the SP to be extracted is a signal received in the past, a condition of t '≦ 0 is obtained.

For example, an example in which the carrier number is 6 (k = 6) and the symbol number is 0 (t = 0) will be described with reference to FIG. In the carrier r (0,6) indicated by the arrow in the figure, since the symbol which received the SP in the closest past is the time point of t = -2, t 'in the expression (1) becomes t' = -2 . Since the example where SP is arrange | positioned every four symbols is shown, SP extracted by SP extracting part 65 is r (-2, 6), r (-6, 6), r (-10, 6), r (-14, 6), ...

Similarly, the SP signal extracted when the carrier number is 12 (k = 12) and the symbol number is 0 (t = 0) is r (0, 12), r (-4, 12), r (-8). , 12), r (-12, 12), ...

The SP extracting section 65 inputs the SP signal extracted by the equation (1) into the time extrapolation section 66. The temporal extrapolation section 66 interpolates the transmission path characteristics at the time of the t symbol based on the extracted SP signal. For that purpose, each extracted SP signal is multiplied by a predetermined coefficient, and these complex addition results are used as interpolation SP signals. When the interpolation SP signal is r '(t, k) and the predetermined coefficient to be multiplied is α,

r '(t, k) = Σα _i × r (t'-4 × i, k)

Becomes

This will be described in more detail with reference to FIG. 8.

8 illustrates a receiving SP and an interpolation SP on a complex plane. The black circle represents the past SP carriers extracted by the SP extracting unit, and the white circle represents the ideal SP reception point in the case of assuming that the SP is received at the time of the t symbol to be interpolated. The asterisk represents the SP signal interpolated by the equation (2). In addition, the solid line indicates past transmission path characteristics, and the dotted line indicates future transmission path characteristics. The SP signal indicated by the black circle is multiplied by a predetermined coefficient α _i , respectively, and complexly added to calculate the signal indicated by the asterisk as interpolation SP. At this time, due to the influence of noise components and high-speed fluctuations, interpolation error components may occur for the ideal SP signal represented by white circles, but when these effects are small, the interpolation error components are kept at a very small level. can do.

Next, a specific design example of the predetermined coefficient α will be described.

First, as a 1st specific example, a primary extrapolation system is demonstrated using FIG.

This is a system in which the number of SPs extracted by the SP extracting unit is set to 2 at maximum, the SP signals are connected in a straight line, and the interpolation SP signals are arranged on the extension line. Therefore, in the case where the terrestrial digital broadcasting system distributed by four symbols is taken as an example, the interpolation SP signal r '(t, k) indicated by an asterisk can be realized by performing the calculation of equation (3).

 r '(t, k) = r (t', k) + c / 4 x {r (t ', k)-r (t'-4, k)}

Here, c has a relationship of c = t-t ', indicating that r (t, k) and r (t', k) are separated by c symbols. In four-symbol dispersion SP, c takes a coefficient from 0 to 3.

A second specific example is shown in FIG. 10. The number of SPs to be extracted is maximum 3, and the interpolation SP is calculated from these SP signals. In the method of the first embodiment, the interpolation error becomes small when the fluctuation rate of the transmission path characteristics is slow, but the error amount increases as the fluctuation speed becomes faster. Therefore, in the second specific example, it is an object to perform high-density interpolation even in an environment where the speed of change is high by using a previous receiving SP in time. The general formula of the second method is multiplied by the coefficients a ₀ to a ₂ so as to be expressed by the equation (4), and then synthesized.

r '(t, k) = a ₀ × r (t', k) + a ₁ × r (t'-4, k) + a ₂ × r (t'-8, k)

Various values can be considered for the selection of the coefficients a ₀ to a ₂ , but equations (5), (6), and the like can be considered as values suitable for the terrestrial digital broadcasting system in which SP carriers are arranged every four symbols.

a ₀ = 1, a ₁ = 0, a ₂ = 0 (for c = 0)

a ₀ = 11/8, a ₁ = -4/8, a ₂ = 1/8 (for c = 1)

a ₀ = 14/8, a ₁ = -8/8, a ₂ = 2/8 (for c = 2)

a ₀ = 17/8, a ₁ = -12/8, a ₂ = 3/8 (for c = 3)

a ₀ = 1, a ₁ = 0, a ₂ = 0 (for c = 0)

a ₀ = 12/8, a ₁ = -6/8, a ₂ = 2/8 (for c = 1)

a ₀ = 16/8, a ₁ = -12 / 8, a ₂ = 4/8 (for c = 2)

a ₀ = 20/8, a ₁ = -18/8, a ₂ = 6/8 (for c = 3)

In this way, the extracted SP signals r (t ', k), r (t'-4, k) and r (t'-8, k) are multiplied by the coefficients shown in the equations (4) to (6). The value indicated by an asterisk is calculated as the interpolation SP signal r '(t, k).

 In the time extrapolation section 66, it is possible to perform interpolation with high density and no delay even for a carrier on which the SP is not arranged by the interpolation method described above. In the terrestrial digital broadcasting system parameter, the SP arranged every 12 carriers can be equivalently set to every three carriers by this interpolation.

In the frequency interpolation section 67, carriers between SP carriers (eg, carriers 0, 3, 6, ... in FIG. 7) interpolated by time extrapolation (eg, carriers 1, 2, 4, 5 in FIG. 7). By interpolating the interpolation filter to interpolate, 7, 8, ...), the transmission path characteristics h (t, k) of the unspecified data carrier of the SP are interpolated. As the interpolation filter, a higher order FIR filter is generally used, but even a simple method such as first order interpolation can be realized.

In addition, from the sampling theorem, the denser the equivalent SP carrier interval, the more it is possible to equalize the multipath of a long delay time. In principle, the multipath up to the delay time shown in equation (7) can be equalized.

(Equalizable Multipath Latency [Sample])

= (Effective symbol length [sample]) / (equivalent SP carrier spacing)

Therefore, as described above, by performing extrapolation in the time direction, densifying the equivalent SP carrier interval, and performing interpolation interpolation in the frequency direction, it is possible to equalize up to a multipath with a long delay time.

 The interpolation transmission line characteristics h (t, k) are calculated by the time extrapolation transmission line characteristic interpolation unit 11 described above.

Since the functions of the delay correction unit 24, the equalizer 26, the re-modulator 27, the D / A 28, and the transmit antenna 29 shown in FIG. 1 are the same as those shown in FIG. Omit.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the second embodiment, the interpolation method of the transmission path characteristics by time extrapolation according to the present invention is applied to the SFN repeater, and the interpolation method is the same as that described in the first embodiment.

The structure shown in FIG. 11 is a structure which replaced the transmission path characteristic interpolation part 25 with the time extrapolation transmission path characteristic interpolation part 11 in the SFN repeater by the prior art shown in FIG. Have. As described above, in the SFN repeater, the FFT unit 23, the channel characteristic interpolation unit 11, the error calculating unit 52, the IFFT unit 53, and the filter coefficient updating unit 54 from the output of the adaptive filter 51 ), A feedback loop input to the adaptive filter 51 is formed again. When the speed of change of the input signal of the adaptive filter 51 is high, the delay time of the feedback loop loses the stability of the loop, and signal degradation such as oscillation occurs. Therefore, by using the interpolation method of transmission path characteristics by time extrapolation according to the present invention, it is possible to shorten the delay time and to follow a signal with a high speed of change.

In addition to the first and second embodiments, the scope of application of the present invention is also applicable to a diversity repeater having a plurality of antennas, a directional control repeater using an adaptive array antenna, or a simple receiver.

In the present invention, when interpolating the characteristics of a transmission path, a plurality of received SPs received in the past are multiplied by different predetermined coefficients, and then the respective results are synthesized and extrapolated in the time direction to reduce the delay time. It becomes possible to plan.

Also in the broadcast wave relay apparatus which receives and relays a broadcast wave, the relay delay time can be shortened, and it is also possible to follow a received signal having a high speed of change.

Claims (9)

In an OFDM reception method of an OFDM receiver, in which an OFDM modulated signal in which a pilot carrier having a known amplitude and phase is distributed in a frequency direction and a time direction is received, The data transmission characteristics of the current data carrier are extrapolated in the time direction by using the data transmission characteristics of q (q is integer) received pilot carriers received in the past p (p is an integer) symbol period, The pilots are arranged by multiplying each result by multiplying a predetermined coefficient with respect to three pilot carriers received at a time point in time past the time extrapolation interpolation is close to the symbol to be interpolated. Characterized by extrapolating extrapolation characteristics of untransmitted symbols in the time direction OFDM reception method. In the OFCM reception method of an OFDM receiver, in which an OFDM modulated signal in which a pilot carrier having a known amplitude and phase is distributed in a frequency direction and a time direction is received, Pilot carriers are arranged by multiplying independent predetermined coefficients by the data transmission characteristics of q (q is integer) received pilot carriers received in the past p (p is an integer) symbol period, and complexly adding the respective results. Extrapolate the data path characteristics of non-data carriers in the time direction, The pilots are arranged by multiplying each result by multiplying a predetermined coefficient with respect to three pilot carriers received at a time point in time past the time extrapolation interpolation is close to the symbol to be interpolated. Characterized by extrapolating extrapolation characteristics of untransmitted symbols in the time direction OFDM reception method. delete delete delete delete The method according to claim 1 or 2, And performing interpolation in the frequency direction after the temporal extrapolation interpolation. OFDM reception method. In an OFDM receiver for receiving an OFDM modulated signal in which a pilot carrier having a known amplitude and phase is distributed in a frequency direction and a time direction, Pilot carriers are arranged by multiplying independent predetermined coefficients by the data transmission characteristics of q (q is integer) received pilot carriers received in the past p (p is an integer) symbol period, and complexly adding the respective results. Either waveform equalization based on transmission characteristic interpolation by extrapolation interpolation in the data direction of data carriers that are not present, or diversity synthesis based on transmission characteristic interpolation by time extrapolation interpolation. And a broadcast wave relay function for converting the post-equalization signal or the diversity synthesis signal back into a modulated signal and retransmitting it as a broadcast wave. OFDM receiver. In an OFDM receiver for receiving an OFDM modulated signal in which a pilot carrier having a known amplitude and phase is distributed in a frequency direction and a time direction, Receive a broadcast wave signal through the reception antenna, multiply the independent predetermined coefficients with respect to the data transmission characteristics of the q (q is integer) received pilot carriers received in the past p (p is an integer) symbol period. And complexly adding the respective results to perform waveform equalization based on the transmission path characteristic interpolation by extrapolation in the time direction of the data transmission characteristics of the data carrier where no pilot carrier is arranged, and re-broadcast the signal after the waveform equalization. Characterized by having a broadcast wave relay function to transmit as a wave OFDM receiver.

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